Copying machines and printers are equipped with a sheet conveyor that individually conveys sheets of a prescribed configuration that are stacked on a tray or cassette so that images of characters, graphs or figures may be recorded on a recording medium having a sheet-like configuration, such as a sheet of printing paper. In a conventional sheet conveyor, the top sheet of the stack of sheets is fed out by means of a paper feed roller, and the sheet thus fed out is sandwiched between a driven conveyance roller which is coaxially situated with respect to the paper feed roller and a driving conveyance roller that is in contact with the driven conveyance roller and that is driven to rotate by means of a motor, such that the sheet is conveyed. In order to ensure conveying force, the driving conveyance roller is pressed onto the driven conveyance roller by means of a spring.
However, the problem described below has been pointed out in connection with conventional sheet conveyors like the one explained above. The sheets being conveyed sometimes cause jamming in a sheet conveyor of this type. Since the sheet conveyor temporarily stops in such a case, it must be restarted after removing the jammed sheets including the sheet that caused the jam. Where a jam occurs while a sheet is being sandwiched between the driven conveyance roller and the driving conveyance roller, the user can see the jammed sheet if he removes the tray or cassette on which sheets are stacked. The user then tends to pull out the jammed sheet toward him by hand (in the direction opposite from the normal conveyance of sheets)
However, since the jammed sheet is being sandwiched between the driven conveyance roller and driving conveyance roller that are in spring-driven pressure contact with each other, the sheet does not slip out easily from between the driven conveyance roller and driving conveyance roller. In addition, since the driving conveyance roller is connected to a motor, it is difficult to rotate it in the reverse direction by pulling the sheet (forcing the roller to rotate in the direction opposite from its normal direction of rotation). Therefore, it is almost impossible for the user to remove the sheet by pulling it out. If he forcibly pulls it out, the sheet becomes torn and a part of it remains in the conveyor, which creates an even more difficult situation. Alternatively, if the user were to attempt to forcibly remove a sheet that had a very high friction coefficient and was difficult to tear, damage could be caused to the gears of the drive system for the driving conveyance roller. Since this would lead to a malfunction in the sheet conveyor, the conveyor would need to be disassembled and repaired before it was restarted. Such a situation can generally occur not only in copying machines or printers, but also in any machine in which a sheet-like object is conveyed while it is being sandwiched.